**Answer : (c) 30º**

Given OA = 3 cm ⇒ OC = 3 cm (radii of the circle)

Also AC = 3 cm ⇒ OA = OC = AC ⇒ ∆ AOC is equilateral

⇒ ∠AOC = 60°.

⇒ ∠ABC = \(\frac{1}{2}\) \(\times\) ∠AOC

**= 30°** (Angle subtended by an arc of a circle at the center is double the angle subtended by it at any point on the remaining part of the circle.)